where \(A = 1, 2, 3, 4\)  is a spinor index and \(\mu = 0, 1, 2, 3, 4\)  is a tensor index. We work with the metric
\(g^{\mu \nu }\)  in \((- + + + +)\)  signature. The representation of gamma matrices used is exactly the one used in
[1]}. We use also the antisymmetric bispinor \(\Omega _{AB}\)  defined in
[1]} to provide an antisymmetric product of two arbitrary spinors \(\xi ^{A}\)  and
\(\chi ^{A}\)  via
\( \xi _{A} \chi ^{A} = \xi ^{A} \Omega _{AB} \chi ^{B} = \xi _{A} \Omega ^{AB} \chi _{B}.\) 
